Marmots will be prepared surgically with chronic arterial, venous and urinary bladder catheters, and renal artery flow probes to determine: 1. Ability of normothermic animals to maximally concentrate urine. 2. Extraction ratio of para-aminohippurate in normothermia and hibernation. 3. Biological half-lives of aldosterone and cortisol during hibernation. 4. Glucose Tm of normothermic animals.